Reveal the complexity of your narrative world with a crowd scene that stops briefly to observe (or dive into the heads of, if you’re using an omniscient POV) multiple members of a crowd. Is it a party? A parade? A protest? A riot? Something more casual and disorganized, like a downtown street corner at lunch hour? Are the people strangers, or do they know each other? Do they have a common purpose, and if not, what connects them? Will this gathering be an event that somehow pushes the story forward or is it simply a piece of world building? Describe people’s clothing, affect, conversation and various reasons for being there. Consider including more than one crowd scene over the span of a larger text and use the differences or similarities to illuminate the development of your character or progression of your story.
Once a sense of the crowd has been established, narrow your focus and zero in some particular character or incident. F. Scott Fitzgerald uses this pattern a couple pages into Chapter 3, the big party scene, of The Great Gatsby:
There was dancing now on the canvas in the garden, old men pushing young girls backward in eternal graceless circles, superior couples holding each other tortuously, fashionably and keeping in the corners—and a great number of single girls dancing individualistically or relieving the orchestra for a moment of the burden of the banjo or the traps. By midnight the hilarity had increased. A celebrated tenor had sung in Italian and a notorious contralto had sung in jazz and between the numbers people were doing "stunts" all over the garden, while happy vacuous bursts of laughter rose toward the summer sky. A pair of stage "twins"—who turned out to be the girls in yellow—did a baby act in costume and champagne was served in glasses bigger than finger bowls. The moon had risen higher, and floating in the Sound was a triangle of silver scales, trembling a little to the stiff, tinny drip of the banjoes on the lawn.
I was still with Jordan Baker. We were sitting at a table with a man of about my age and a rowdy little girl who gave way upon the slightest provocation to uncontrollable laughter. I was enjoying myself now. I had taken two finger bowls of champagne and the scene had changed before my eyes into something significant, elemental and profound.